This feature was actually implemented on Bug 93888 and then removed on Web Inspector UI revamp landed after Blink's fork so I am filling another issue as a request for revival of the work has been done there inside WebKit!
My request originally there,
> It would be nice if inspector could make hidden characters (like ‎ ‏ ‌ ‍ ...) visible and show them to web developer for better debugging.
> You can see list of hidden characters on http://getfirebug.com/developer/api/firebug1.6X/symbols/src/content_firebug_lib.js.html line 2186 to 2194.
After the fork I've filed https://crbug.com/463642 and https://crbug.com/460044 against Chrome so the list eventually ended up to be https://source.chromium.org/chromium/chromium/src/+/master:third_party/devtools-frontend/src/front_end/elements/ElementsTreeOutline.js;l=1679?q=MappedCharToEntity&ss=chromium which I think it is safe to use the updated here instead.
I'll try to send a patch about this (actually it is as easy as https://pastebin.com/1hVMRLD3 ) however others are also welcomed if I happened to forget about this.
Oops, https://bugs.webkit.org/show_bug.cgi?id=181302 also filed in the meanwhile, will merge one to another.
*** This bug has been marked as a duplicate of bug 181302 ***